Communication apparatus and communication method for configuring resource region candidates and mapping downlink control information to same

ABSTRACT

In a base station ( 100 ), a division number calculating unit ( 103 ) calculates the division number of a PRB pair on the basis of a first number of REs capable of mapping an allocation control signal, a second number of REs capable of mapping signals other than the allocation control signal, and a reference value, which is the number of REs satisfying the reception quality request in a terminal ( 200 ) for the allocation control signal, in each PRB pair. Then, a control signal mapping control unit ( 104 ) determines a search space by determining a control channel element group constituting a plurality of mapping unit resource region candidates within a CCE group obtained by separating each PRB pair contained in a first group into the same number as the division number.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/370,814, filed Dec. 6, 2016, which is a continuation of U.S.patent application Ser. No. 15/059,204, filed Mar. 2, 2016, now U.S.Pat. No. 9,554,380, which is a continuation of U.S. patent applicationSer. No. 14/122,585, filed Nov. 26, 2013, now U.S. Pat. No. 9,313,777,which is a U.S. National-Stage Entry of International Patent ApplicationNo. PCT/JP2012/004786 filed Jul. 27, 2012, which claims priority fromJapan Patent Application No. 2011-176855 filed Aug. 12, 2011.

BACKGROUND Technical Field

The present invention relates to a transmission apparatus, a receptionapparatus, a transmission method, and a reception method.

Description of the Related Art

In recent years, it has become common to transmit not only audio databut also large-volume data, such as still image data and moving imagedata in addition to audio data in cellular mobile communication systems,in response to spread of multimedia information. Active studiesassociated with techniques for achieving a high transmission rate in ahigh-frequency radio band have been conducted to achieve large-volumedata transmission.

When a high frequency radio band is utilized, however, attenuationincreases as the transmission distance increases, although a highertransmission rate can be expected within a short range. Accordingly, thecoverage area of a radio communication base station apparatus(hereinafter, abbreviated as “base station”) decreases when a mobilecommunication system using a high frequency radio band is actually putinto operation. Thus, more base stations need to be installed in thiscase. The installation of base stations involves reasonable costs,however. For this reason, there has been a high demand for a techniquethat provides a communication service using a high-frequency radio bandwhile limiting an increase in the number of base stations.

In order to meet such a demand, studies have been carried out on a relaytechnique in which a radio communication relay station apparatus(hereinafter, abbreviated as “relay station”) is installed between abase station and a radio communication mobile station apparatus(hereinafter, abbreviated as “mobile station”) to perform communicationbetween the base station and mobile station via the relay station forthe purpose of increasing the coverage area of each base station. Theuse of relay technique allows a mobile station not capable of directlycommunicating with a base station to communicate with the base stationvia a relay station.

It is required for an LTE-A (long-term evolution advanced) system forwhich the introduction of the relay technique described above has beenstudied, to maintain compatibility with LTE (long-term evolution) interms of a smooth transition from and coexistence with LTE. For thisreason, mutual compatibility with LTE is required for the relaytechnique as well.

FIG. 1 illustrates example frames in which control signals and data areassigned in the LTE system and the LTE-A system.

In the LTE system, DL (downlink) control signals from a base station toa mobile station are transmitted through a DL control channel, such asPDCCH (physical downlink control channel). In LTE, DL grant (alsoreferred to as “DL assignment”) indicating DL data assignment and UL(uplink) grant indicating UL data assignment are transmitted throughPDCCH. A DL grant indicates that a resource in the subframe in which theDL grant is transmitted has been allocated to the mobile station.Meanwhile, in an FDD system, a UL grant indicates that a resource in thefourth subframe after the subframe in which the UL grant is transmittedhas been allocated to the mobile station. In a TDD system, a UL grantindicates that the resource in a subframe transmitted after four or moresubframes from the subframe in which the UL grant is transmitted hasbeen allocated to the mobile station. In the TDD system, the subframe tobe assigned to the mobile station, or the number of subframes before theassigned subframe in which the UL grant is transmitted is determined inaccordance with the time-division pattern of the UL and DL (hereinafterreferred to as “UL/DL configuration pattern”). Regardless of the UL/DLconfiguration pattern, the UL subframe is a subframe after at least foursubframes from the subframe in which the UL grant is transmitted.

In the LTE-A system, relay stations, in addition to base stations, alsotransmit control signals to mobile stations in PDCCH regions in the topparts of subframes. With reference to a relay station, DL controlsignals have to be transmitted to a mobile station. Thus, the relaystation switches the processing to reception processing aftertransmitting the control signals to the mobile station to prepare forreceiving signals transmitted from the base station. The base station,however, transmits DL control signals to the relay station at the timethe relay station transmits the DL control signals to the mobilestation. The relay station therefore cannot receive the DL controlsignals transmitted from the base station. In order to avoid suchinconvenience in LTE-A, studies have been carried out on providing aregion for mapping downlink control signals for relay stations (i.e.,relay PDCCH (R-PDCCH) region) in a data region as illustrated in FIG. 2in LTE-A. Similar to the PDCCH, mapping a DL grant and UL grant to theR-PDCCH is studied. In the R-PDCCH, as illustrated in FIG. 1, mapping aDL grant in the first slot and a UL grant in the second slot is studied(refer to Non-patent Literature 1). Mapping the DL grant only in thefirst slot reduces a delay in decoding the DL grant and allows relaystations to prepare for ACK/NACK transmission for DL data (transmittedin the fourth subframes following reception of DL grant in FDD). Eachrelay station finds the downlink control signals intended for the relaystation by performing blind-decoding on downlink control signalstransmitted using an R-PDCCH region from a base station within aresource region indicated using higher layer signaling from the basestation (i.e., search space). As described above, the base stationnotifies the relay station of the search space corresponding to theR-PDCCH by higher layer signaling.

Given the introduction of various apparatuses as radio communicationterminals in the future M2M (machine to machine) communication, forexample, there is a concern for a shortage of resources in the mappingregion for PDCCH (i.e., “PDCCH region”) due to an increase in the numberof terminals. If PDCCH cannot be mapped due to such a resource shortage,the DL data cannot be assigned for the terminals. Thus, the resourceregion for mapping DL data (i.e., “PDSCH (physical downlink sharedchannel) region”) cannot be used even if there is an available region,which may cause a decrease in the system throughput. Studies have beencarried out to solve such resource shortage through mapping controlsignals for terminals served by a base station also in a data region towhich R-PDCCH is mapped. The resource region to which control signalsfor terminals served by the base station are mapped and which can beutilized as a data region at different timings is called an “enhancedPDCCH (E-PDCCH) region, “new-PDCCH (N-PDCCH) region” or “X-PDCCH region”or the like. As described above, in LTE-A, a relay technique isintroduced and relay control signals are mapped to the data region.Since the relay control signal may be expanded and used as a controlsignal for a terminal, the resource region to which control signals forterminals served by the base station are mapped and which can beutilized as a data region at different timings is also called “R-PDCCH.”Mapping the control signals (i.e., E-PDCCH) to a data region in such amanner enables transmission power control for control signalstransmitted to terminals near a cell edge or interference control forinterference to another cell by control signals to be transmitted or forinterference to the cell from another cell. In LTE-Advance, a hightransmission rate is achieved using a wideband radio bandwidth,multiple-input multiple-output (MIMO) transmission technique andinterference control technique.

PDCCH and R-PDCCH have four aggregation levels, i.e., levels 1, 2, 4,and 8 (for example, refer to Non-patent Literature (hereinafter,abbreviated as “NPL”) 1). Levels 1, 2, 4, and 8 respectively have six,six, two, and two “resource region candidates.” The term “resourceregion candidate” refers to a candidate region to which control signalsare to be mapped. Each resource region candidate is composed of as manycontrol channel elements (CCE) as corresponding aggregation levels. Inaddition, when a single terminal is set with one aggregation level,control signals are actually mapped to one of the multiple resourceregion candidates of the aggregation level. FIG. 2 illustrates examplesearch spaces corresponding to R-PDCCH. The ovals represent searchspaces at various aggregation levels. The multiple resource regioncandidates in the search spaces at the different aggregation levels arearranged consecutively on VRBs (virtual resource blocks). The resourceregion candidates in the VRBs are mapped to PRBs (physical resourceblocks) through higher layer signaling.

A search space corresponding to E-PDCCH is a resource region to whichcontrol signals transmitted from a base station to a terminal may bemapped. A search space corresponding to E-PDCCH is individually set foreach terminal.

As described above, in the R-PDCCH region, a DL grant is mapped to thefirst slot and UL grant is mapped to the second slot. That is, theresource to which the DL grant is mapped is separated from the resourceto which the UL grant is mapped in the time domain. In contrast, inE-PDCCH, as shown in FIG. 3, studies are also underway to separate theresource to which the DL grant is mapped from the resource to which theUL grant is mapped in the frequency domain (that is, subcarriers or PRBpair). Here, the term “PRB (physical resource block) pair” refers to aset of PRBs of the first slot and the second slot, whereas the term“PRB” refers to each of the PRBs of the first slot and the second slot.

For the design of E-PDCCH, part of the design of R-PDCCH may be used ora design completely different from the design of R-PDCCH may be used.Actually, studies are underway to make the design of E-PDCCH differentfrom the design of R-PDCCH.

CITATION LIST Non-Patent Literature

NPL 1

3GPP TS 36.216 V10.1.0 Physical layer for relaying operation

BRIEF SUMMARY Technical Problem

When the resource to which a DL grant is mapped is separated from theresource to which a UL grant is mapped in the frequency domain (that is,subcarriers or RB pair), one PRB pair may be designated as a minimumunit (that is, a CCE) when resources are allocated to E-PDCCH. However,when a PRB pair made up of two slots is designated as a CCE, theresource amount of CCE increases. For this reason, a reception SINR ofE-PDCCH increases and the possibility of receiving quality becomingexcessively high, which results in an increased possibility of resourcesbeing wasted. Therefore, a “divided resource region” obtained bydividing one PRB pair may be used as a CCE of E-PDCCH.

However, when the division number per PRB pair increases, the resourceamount of CCE for E-PDCCH (that is, the number of resource elements(REs) forming one CCE) decreases. Moreover, when the aggregation levelof E-PDCCH is assumed to be 1, 2, 4 or 8 as in the cases of PDCCH andR-PDCCH, the number of terminals that can be supported decreases. Thatis, the receiving quality of terminals that can be supported isdetermined by the receiving quality of highest aggregation level 8. Whenthe resource amount of CCE for E-PDCCH is small, the receiving qualityof E-PDCCH degrades, and therefore the number of terminals that satisfythe desired receiving quality decreases.

Furthermore, even when the division number per PRB pair is fixed, thenumber of REs forming a CCE varies from one subframe to another. Thefollowing is the description of factors that cause the number of REsforming a CCE to vary from one subframe to another even when thedivision number per PRB pair is fixed. In LTE and LTE-A, one PRB has 12subcarriers in the frequency direction and has a width of 0.5 msec inthe time direction as shown in FIG. 4. A unit of two PRBs combined inthe time direction is called a “PRB pair.” That is, a PRB pair has 12subcarriers in the frequency direction and has a width of 1 msec in thetime direction. However, when a PRB pair represents a block of 12subcarriers in the frequency domain, the PRB pair may be simply called“RB.” In addition, a unit defined by one subcarrier and one OFDM symbolis a resource element (RE). The items described about PRBs here alsoapply to VRBs. The term “RB” is used to generically call a PRB and VRB.

[1] CP length of OFDM symbol:

The number of OFDM symbols per PRB varies depending on a CP (cyclicprefix) length of OFDM symbol. Therefore, the number of REs forming aCCE varies depending on the CP (cyclic prefix) length even if thedivision number per PRB pair is fixed.

To be more specific, a normal downlink subframe includes 14 OFDM symbolsin the case of a normal CP and includes 12 OFDM symbols in the case ofan extended CP. Furthermore, a DwPTS region of a special subframe shownin FIG. 5 (that is, region used for DL transmission) includes three,nine, ten, eleven or twelve OFDM symbols in the case of a normal CP andthree, eight, nine or ten OFDM symbols in the case of an extended CP.

[2] Number of REs used for reference signal (RS):

The number of REs to which reference signals are mapped in one PRBvaries from one subframe to another. Therefore, the number of REsforming a CCE varies depending on the number of REs to which referencesignals are mapped in one PRB even when the division number per PRB pairis fixed.

(1) CRS:

CRS is transmitted in all RBs. Although CRS is also transmitted in adata region in subframes other than MBSFN subframes, CRS is transmittedusing only two initial OFDM symbols in MBSFN subframes.

(2) DMRS (12 REs, 24 REs or 16 REs):

The use of DMRS is dynamically indicated from a base station to aterminal using downlink assignment control information (DL assignment).The number of DMRSs to be set can be made to vary from one user toanother. DMRS is transmitted in a data region and the value to be setmay vary from one RB to another.

(3) CSI-RS (2 REs or more):

CSI-RS is transmitted in all RBs. A subframe to be transmitted isdetermined by a previously set period. CSI-RS has a muting function ofnot transmitting data in order to receive a CSI-RS of another cell. Oncethe CSI-RS muting is set, the number of REs usable as a data region orE-PDCCH region further decreases.

(4) PRS (positioning reference signals):

PRS (positioning reference signals) is an RS used for positionmeasurement. In such a setting that REs set for this PRS is not used forthe E-PDCCH region, the number of REs available for E-PDCCH furtherdecreases.

[3] Number of OFDM symbols forming PDCCH region:

The number of OFDM symbols used for PDCCH is variable from one to four.Therefore, in such a setting that the PDCCH region is not used forE-PDCCH, the number of OFDM symbols available for E-PDCCH decreases asthe number of OFDM symbols of the PDCCH region increases. That is, thenumber of REs forming a CCE varies depending on the number of OFDMsymbols forming the PDCCH region even if the division number per PRBpair is fixed.

FIG. 6 and FIG. 7 illustrate the number of REs of the first slot and thesecond slot when resources of the fourth and subsequent OFDM symbols ofthe PRB pair are used for E-PDCCH. FIG. 6 and FIG. 7 illustrate anexample where CSI-RS is mapped to the second slot in particular. FIG. 6and FIG. 7 together form one table: FIG. 6 showing the first half of thetable and FIG. 7 showing the second half of the table.

As described above, when the number of REs located in a PRB pair andavailable for E-PDCCH fluctuates considerably, receiving quality of acontrol signal is more likely to degrade.

An object of the present invention is to provide a transmittingapparatus, a receiving apparatus, a transmission method and a receptionmethod that are capable of improving receiving quality of a controlsignal.

Solution to Problem

A transmitting apparatus according to an aspect of the present inventionincludes: a calculation section that calculates a division number ofeach one of physical channel resource blocks based on: a first number ofresource elements in a corresponding one of the physical channelresource blocks to which resource elements an assignment control signalis capable of being mapped; a second number of resource elements towhich a signal other than the assignment control signal is mapped; and areference value which is a number of resource elements that satisfyreceiving quality of the assignment control signal in a receivingapparatus; a control section that sets a resource region candidateincluding at least one control channel element obtained by dividing eachone of the physical channel resource blocks into the division number andthat determines, based on an aggregation level, a search space made upof a plurality of the resource region candidates set in each one of thephysical channel resource blocks; and a transmitting section thattransmits, to the receiving apparatus, the assignment control signalmapped in one of the plurality of resource region candidates forming thesearch space.

A receiving apparatus according to an aspect of the present inventionincludes: a calculation section that calculates a division number ofeach one of physical channel resource blocks based on: a first number ofresource elements in a corresponding one of the physical channelresource blocks to which resource elements an assignment control signalis capable of being mapped; a second number of resource elements towhich a signal other than the assignment control signal is mapped; and areference value which is a number of resource elements that satisfyreceiving quality of the assignment control signal in a receivingapparatus; an identification section that sets a resource regioncandidate including at least one control channel element obtained bydividing each one of the physical channel resource blocks into thedivision number and that identifies, based on an aggregation level, asearch space made up of a plurality of the resource region candidatesset in each one of the physical channel resource blocks; and a receivingsection that receives the assignment control signal mapped in one of theplurality of resource region candidates forming the identified searchspace.

A transmission method according to an aspect of the present inventionincludes: calculating a division number of each one of physical channelresource blocks based on: a first number of resource elements in acorresponding one of the physical channel resource blocks to whichresource elements an assignment control signal is capable of beingmapped; a second number of resource elements to which a signal otherthan the assignment control signal is mapped; and a reference valuewhich is the number of resource elements that satisfy receiving qualityof the assignment control signal in a receiving apparatus; setting aresource region candidate including at least one control channel elementobtained by dividing each one of the physical channel resource blocksinto the division number; determining, based on an aggregation level, asearch space made up of a plurality of the resource region candidatesset in each one of the physical channel resource blocks; andtransmitting, to the receiving apparatus, the assignment control signalmapped in one of the plurality of resource region candidates forming thesearch space.

A reception method according to an aspect of the present inventionincludes: calculating a division number of each one of physical channelresource blocks based on: a first number of resource elements in acorresponding one of the physical channel resource blocks to whichresource elements an assignment control signal is capable of beingmapped; a second number of resource elements to which a signal otherthan the assignment control signal is mapped; and a reference valuewhich is the number of resource elements that satisfy receiving qualityof the assignment control signal; setting a resource region candidateincluding at least one control channel element obtained by dividing eachone of the physical channel resource blocks into the division number;identifying ,based on an aggregation level, a search space made up of aplurality of the resource region candidates set in each one of thephysical channel resource blocks; and receiving the assignment controlsignal mapped in one of the plurality of resource region candidatesforming the identified search space.

Advantageous Effects of Invention

According to the present invention, it is possible to provide atransmitting apparatus, a receiving apparatus, a transmission method anda reception method that are capable of improving receiving quality of acontrol signal.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 illustrates example frames containing control signals and dataassigned thereto, in the LTE system and the LTE-A system;

FIG. 2 illustrates example search spaces corresponding to R-PDCCH;

FIG. 3 illustrates an example of mapping whereby a resource to which DLgrant is mapped is separated from a resource to which UL grant is mappedin the frequency domain;

FIG. 4 is a diagram provided for describing PRB pairs;

FIG. 5 illustrates a special subframe;

FIG. 6 illustrates the number of REs of a first slot and a second slotwhen resources of the fourth and subsequent OFDM symbols of a PRB pairare used for E-PDCCH;

FIG. 7 illustrates the number of REs of a first slot and a second slotwhen resources of the fourth and subsequent OFDM symbols of a PRB pairare used for E-PDCCH;

FIG. 8 is a block diagram illustrating a main configuration of a basestation according to Embodiment 1 of the present invention;

FIG. 9 is a block diagram illustrating a main configuration of aterminal according to Embodiment 1 of the present invention; FIG. 10 isa block diagram illustrating a configuration of the base stationaccording to Embodiment 1 of the present invention;

FIG. 11 is a block diagram illustrating a configuration of the terminalaccording to Embodiment 1 of the present invention;

FIG. 12 is a block diagram illustrating a configuration of a controlsignal mapping control section according to Embodiment 2 of the presentinvention;

FIG. 13 is a block diagram illustrating a configuration of an extractedresource identification section according to Embodiment 2 of the presentinvention;

FIG. 14 is a diagram provided for describing the operations of a basestation and a terminal according to Embodiment 2 of the presentinvention;

FIG. 15 is a block diagram illustrating a configuration of a controlsignal mapping control section according to Embodiment 3 of the presentinvention;

FIG. 16 is a block diagram illustrating a configuration of an extractedresource identification section according to Embodiment 3 of the presentinvention;

FIG. 17 is a diagram provided for describing the operations of a basestation and a terminal according to Embodiment 3 of the presentinvention; and

FIG. 18 is a diagram provided for describing the operations of a basestation and a terminal according to Embodiment 4 of the presentinvention.

DETAILED DESCRIPTION

Embodiments of the present invention will be described in detail withreference to the drawings. In the embodiments, the same elements will beassigned the same reference numerals, and any duplicate description ofthe elements is omitted.

Embodiment 1 Overview of Communication System

A communication system according to Embodiment 1 of the presentinvention includes a transmitting apparatus and a receiving apparatus.Specifically, in this embodiment of the present invention, a descriptionwill be provided while the transmitting apparatus is referred to as basestation 100, and the receiving apparatus is referred to as terminal 200.The communication system is an LTE-A system, for example. Base station100 is an LTE-A base station, and terminal 200 is an LTE-A terminal, forexample.

FIG. 8 is a block diagram illustrating a main configuration of basestation 100 according to Embodiment 1 of the present invention.

Base station 100 maps an assignment control signal to one of a pluralityof “resource region candidates” forming a search space and transmits themapped signal to terminal 200. Each resource region candidate iscomposed of as many CCEs as the value of aggregation level.

Division number calculation section 103 calculates the division numberof a PRB pair based on a first number of REs to which an assignmentcontrol signal in each PRB pair can be mapped, a second number of REs towhich a signal other than the assignment control signal is mapped and areference value. The reference value is the number of REs that satisfyreceiving quality requirements of the assignment control signal interminal 200.

Control signal mapping control section 104 sets resource regioncandidates including at least one CCE obtained by dividing each PRB pairby the division number and determines a search space configured of aplurality of resource region candidates set for each PRB pair based onan aggregation level.

The assignment control signal is mapped by mapping section 107 to one ofa plurality of “resource region candidates” forming a search spacedetermined in control signal mapping control section 104 and transmittedto terminal 200.

FIG. 9 is a block diagram illustrating a main configuration of terminal200 according to Embodiment 1 of the present invention.

Terminal 200 receives an assignment control signal mapped by atransmitting apparatus to one of a plurality of “resource regioncandidates” forming a search space. Each “resource region candidate” ismade up of as many control channel elements as the value of aggregationlevel.

Division number calculation section 205 calculates the division numberof a PRB pair based on a first number of REs to which an assignmentcontrol signal in each PRB pair can be mapped, a second number of REs towhich a signal other than the assignment control signal is mapped and areference value. The reference value is the number of REs that satisfyreceiving quality requirements of the assignment control signal interminal 200.

Extracted resource identification section 206 sets resource regioncandidates including at least one CCE obtained by dividing each PRB pairby the division number and identifies a search space made up of theplurality of resource region candidates set in each PRB pair based onthe aggregation level. The plurality of “resource region candidates”forming the identified search space correspond to a plurality of“resource regions to be extracted.” The assignment control signal mappedby the transmitting apparatus to one of the plurality of identified“resource region candidates” is extracted by signal demultiplexingsection 202, and the assignment control signal is thereby received.

Configuration of Base Station 100

FIG. 10 is a block diagram illustrating a configuration of base station100 according to Embodiment 1 of the present invention. In FIG. 10, basestation 100 includes assignment control information generating section101, search space determining section 102, division number calculationsection 103, control signal mapping control section 104,error-correction coding section 105, modulation section 106, mappingsection 107, transmitting section 108, receiving section 109,demodulation section 110, and error-correction decoding section 111.

When there are a data signal to be transmitted and a data signal to beassigned to an uplink, assignment control information generating section101 determines a resource to which the data signal is assigned andgenerates assignment control information (DL assignment and UL grant).The DL assignment includes information on mapping resources of adownlink data signal. On the other hand, the UL grant includesinformation on mapping resources of uplink data to be transmitted fromterminal 200. The DL assignment is outputted to mapping section 107 andthe UL grant is outputted to receiving section 109.

Search space determining section 102 determines a PRB pair candidategroup (that is, corresponding to the above-described first group, andhereinafter may also be referred to as “search space PRB group”) towhich a control signal including at least one of DL grant and UL granttransmitted to terminal 200 and outputs information on the determined“search space PRB group” (hereinafter, may also be referred to as“search space information”) to control signal mapping control section104 and error-correction coding section 105.

The information on the “search space PRB group” is a bit stringcomposed, for example, of N bits and the N bits respectively correspondto N PRB pairs forming a communication band available to base station100. For example, a PRB pair corresponding to bit value 1 is a PRB pairincluded in a search space and a PRB pair corresponding to bit value 0is a PRB pair not included in the search space.

Division number calculation section 103 receives the number of OFDMsymbols available for E-PDCCH in one PRB pair and the number of REs usedfor RS in one PRB pair as input and calculates the division number D bywhich one PRB pair is divided based on these numbers. This divisionnumber D is calculated for each subframe because the number of REsavailable for E-PDCCH included in one PRB pair may vary from onesubframe to another. The PRB pair is divided based on the calculateddivision number D, and D “divided resource regions” are thereby defined.Each divided resource region is used as a CCE of E-PDCCH.

To be more specific, the division number D is calculated from equation 1below.(Equation 1)Division number=Number of REs available for E-PDCCH/M   [1]

M is a lower limit value of the number of REs forming one CCE necessaryto satisfy receiving quality requirements in the terminal.

The number of REs available for E-PDCCH can be calculated from equation2 below.(Equation 2)Number of REs available for E-PDCCH=(number of OFDM symbols availablefor E-PDCCH in PRB pair)×(12 subcarriers)−(number of REs used for otherthan E-PDCCH in resource region defined by number of OFDM symbolsavailable for E-PDCCH in PRB pair)   [2]

The number of REs used for other than E-PDCCH in the resource regiondefined by the number of OFDM symbols available for E-PDCCH in the PRBpair is calculated, for example, by equation 3 below.(Equation 3)(Number of REs used for other than E-PDCCH in resource region defined bynumber of OFDM symbols available for E-PDCCH in PRB pair)=(number of REsused for DMRS in symbols used for E-PDCCH)−(number of muting set REs ofCSI-RS in symbols used for E-PDCCH)   [3]

When PRS is taken into consideration, the number of REs used for PRS isfurther subtracted in symbols used for E-PDCCH.

Control signal mapping control section 104 determines a search spacecorresponding to a pair of the division number M calculated in divisionnumber calculation section 103 and an aggregation level based on thedivision number M, “search space information” received from search spacedetermining section 102 and the aggregation level. Control signalmapping control section 104 selects one of a plurality of “resourceregion candidates” forming the determined search space as a “controlsignal mapping resource.” Here, the “control signal mapping resource” isa resource region to which a control signal intended for terminal 200 isactually mapped. Furthermore, each “resource region candidate” is madeup of as many CCEs as aggregation levels. Furthermore, the “controlsignal mapping resource” is also made up of as many CCEs as aggregationlevels. However, although the number of REs forming a CCE normallyvaries depending on the division number M, it is leveled.

Error-correction coding section 105 receives the transmission datasignal and the search space information as input, performserror-correction coding on the inputted signal and outputs the codedsignal to modulation section 106.

Modulation section 106 applies modulation processing to the signalreceived from error-correction coding section 105 and outputs themodulated data signal to mapping section 107.

Mapping section 107 maps the assignment control information generated inassignment control information generating section 101 to the “controlsignal mapping resource” determined in control signal mapping controlsection 104.

Furthermore, mapping section 107 maps the data signal received frommodulation section 106 to a downlink resource corresponding to thedownlink resource allocation control information (DL assignment)generated in assignment control information generating section 101.

The assignment control information and the data signal are mapped topredetermined resources in this way, and a transmission signal isthereby formed. The transmission signal thus formed is outputted totransmitting section 108.

Transmitting section 108 applies radio transmission processing such asup-conversion to the input signal and transmits the signal to terminal200 via an antenna.

Receiving section 109 receives the signal transmitted from terminal 200and outputs the received signal to demodulation section 110. To be morespecific, receiving section 109 separates a signal corresponding to aresource indicated by UL grant from the received signal, appliesreception processing such as down-conversion to the separated signal andoutputs the signal to demodulation section 110.

Demodulation section 110 applies demodulation processing to the inputsignal and outputs the signal obtained to error-correction decodingsection 111.

Error-correction decoding section 111 decodes the input signal andobtains a received data signal from terminal 200.

Configuration of Terminal 200

FIG. 11 is a block diagram illustrating a configuration of terminal 200according to Embodiment 1 of the present invention. In FIG. 11, terminal200 includes receiving section 201, signal demultiplexing section 202,demodulation section 203, error-correction decoding section 204,division number calculation section 205, extracted resourceidentification section 206, control signal receiving section 207,error-correction coding section 208, modulation section 209, mappingsection 210, and transmitting section 211.

Receiving section 201 receives a signal transmitted from base station100, applies reception processing such as down-conversion thereto andthen outputs the signal to signal demultiplexing section 202.

Signal demultiplexing section 202 extracts, from the received signal, asignal corresponding to a “resource region group to be extracted”indicated by an “extraction indication signal” received from extractedresource identification section 206 and outputs the extracted signal tocontrol signal receiving section 207. The “resource region group to beextracted” corresponds to the “resource region candidate group”determined in control signal mapping control section 104.

Furthermore, signal demultiplexing section 202 extracts a signalcorresponding to a data resource indicated by DL assignment outputtedfrom control signal receiving section 207 (that is, downlink datasignal) from the received signal and outputs the extracted signal todemodulation section 203.

Demodulation section 203 demodulates the signals from signaldemultiplexing section 202 and outputs the demodulated signals toerror-correction decoding section 204.

Error-correction decoding section 204 decodes the demodulated signalsoutputted from demodulation section 203 and outputs the decoded receiveddata signals. Specifically, error-correction decoding section 204outputs search space information transmitted from base station 100 toextracted resource identification section 206.

Division number calculation section 205 has the same function as that ofdivision number calculation section 103. That is, division numbercalculation section 205 receives the number of OFDM symbols availablefor E-PDCCH in one PRB pair and the number of REs available for RS inone PRB pair as input and calculates the division number D by which onePRB pair is divided based on these numbers. The PRB pair is dividedbased on the calculated division number D and D “divided resourceregions” are thereby defined. Each divided resource region is used as aCCE of E-PDCCH. The number of REs used by CRS in one PRB pair isindicated from base station 100 to terminal 200 through a broadcastchannel. The number of REs used by DMRS in one PRB pair may vary fromone terminal to another. Therefore, the number of REs used by DMRS maybe previously specified from base station 100 to terminal 200 by ahigher layer control signal during E-PDCCH transmission. Furthermore,the number of REs and the period used by CSI-RS in one PRB pair arespecified from base station 100 to terminal 200 by a higher layercontrol signal for each terminal.

Extracted resource identification section 206 identifies a plurality of“resource regions to be extracted” (that is, search spaces)corresponding to a pair of the division number M calculated in divisionnumber calculation section 205 and an aggregation level based on thedivision number M, the search space information transmitted from basestation 100 and the aggregation level. Extracted resource identificationsection 206 outputs information on the plurality of identified “resourceregions to be extracted” to signal demultiplexing section 202 as an“extraction indication signal.”

Control signal receiving section 207 performs blind decoding on thesignal received from signal demultiplexing section 202 and therebydetects a control signal (DL assignment or UL grant) intended forterminal 200 of control signal receiving section 207. The detected DLassignment intended for terminal 200 is outputted to signaldemultiplexing section 202 and the detected UL grant intended forterminal 200 is outputted to mapping section 210.

Error-correction coding section 208 uses the transmission data signalsas input, performs error-correction coding on the transmission datasignals, and outputs the coded signal to modulation section 209.

Modulation section 209 modulates the signal outputted fromerror-correction coding section 208 and outputs the modulated signal tomapping section 210.

Mapping section 210 maps the signal outputted from modulation section209 according to the UL grant received from control signal receivingsection 207 and outputs the mapped signal to transmitting section 211.

Transmitting section 211 applies transmission processing such asup-conversion to the input signal and transmits the signal.

Operations of Base Station 100 and Terminal 200

The operations of base station 100 and terminal 200 configured in themanner described above will be described.

<Division Number Calculation Processing by Base Station 100>

Division number calculation section 103 in base station 100 receives thenumber of OFDM symbols available for E-PDCCH in one PRB pair and thenumber of REs used for RS in one PRB pair as input and calculates thedivision number D by which one PRB pair is divided based on thesenumbers. D “divided resource regions” are defined by dividing the PRBpair based on the calculated division number D. Each divided resourceregion is used as a CCE of E-PDCCH.

To be more specific, the division number is calculated using equation 1described above. That is, the division number is calculated based on the“reference number of REs” and the number of REs that can be used forE-PDCCH in the PRB pair to be calculated so that the number of REsforming each CCE becomes at least equal to the “reference number ofREs.” Even when the number of REs per PRB pair varies from one subframeto another, this allows the number of REs per PRB pair to be leveledamong subframes, thus making it possible to secure receiving quality perCCE to a certain level or higher. That is, even when transmittingassignment control information to a terminal of poor receiving qualitylocated near the cell edge, it is possible to use subframes having fewerREs per PRB pair. However, when the division number calculated accordingto equation 1 described above is zero, “1” is used as the divisionnumber. Furthermore, when the value that the division number can take islimited to 1, 2 or 4, “2” is used as the division number when thedivision number calculated by equation 1 is “3.”

<Control Signal Mapping Resource Determination Processing by BaseStation 100>

Control signal mapping control section 104 in base station 100determines a search space corresponding to a pair of the division numberM and the aggregation level based on the division number M calculated indivision number calculation section 103, “search space information”received from search space determining section 102 and the aggregationlevel. Control signal mapping control section 104 then selects one ofthe plurality of “resource region candidates” forming the determinedsearch space as a “control signal mapping resource.” By being mapped tothe determined control signal mapping resource, the assignment controlinformation generated in assignment control information generatingsection 101 is transmitted from base station 100 to terminal 200.

<Division Number Calculation Processing by Terminal 200>

Division number calculation section 205 in terminal 200 receives thenumber of OFDM symbols available for E-PDCCH in one PRB pair and thenumber of REs used for RS in one PRB pair as input, and calculates thedivision number D by which one PRB pair is divided based on thesenumbers. D “divided resource regions” are defined by dividing the PRBpair based on the calculated division number D.

<Extracted Resource Identification Processing by Terminal 200>

Extracted resource identification section 206 in terminal 200 identifiesa plurality of “resource regions to be extracted” (that is, searchspaces) corresponding to a pair of the division number M and theaggregation level based on the division number M calculated in divisionnumber calculation section 205, the search space information transmittedfrom base station 100 and the aggregation level. Signals correspondingto the plurality of identified “resource regions to be extracted” in thereceived signal are subjected to blind decoding processing in controlsignal receiving section 207.

As described above, according to the present embodiment, division numbercalculation section 103 in base station 100 calculates the divisionnumber of a PRB pair based on a first number of REs to which anassignment control signal in each PRB pair can be mapped, a secondnumber of REs to which a signal other than the assignment control signalis mapped and a reference value. The reference value is the number ofREs that satisfy receiving quality requirements of the assignmentcontrol signal in terminal 200.

Control signal mapping control section 104 determines a search space bydetermining a control channel element group (that is, a physical channelCCE group used) forming a plurality of resource region candidates amongCCE groups obtained by dividing each PRB pair included in the firstgroup by the same number as the division number.

In this manner, the number of REs included in a CCE can be leveled evenwhen there is a variation in the number of REs which are included in thePRB pair and to which an assignment control signal can be mapped. Thismakes it possible to improve receiving quality of the control signal.

According to the present embodiment, division number calculation section205 in terminal 200 calculates the division number of a PRB pair basedon a first number of REs to which an assignment control signal in eachPRB pair can be mapped, a second number of REs to which a signal otherthan the assignment control signal is mapped and a reference value. Thereference value is the number of REs that satisfy receiving qualityrequirements of the assignment control signal in terminal 200.

Extracted resource identification section 206 identifies a search spaceby identifying a control channel element group forming a plurality of“resource region candidates” in a CCE group obtained by dividing eachPRB pair included in the first group set in base station 100 into thesame number as the division number. The plurality of “resource regioncandidates” forming the identified search space, correspond to aplurality of “resource regions to be extracted.”

Embodiment 2

Embodiment 2 relates to a method for mapping a logical channel (VRB) toa physical channel (PRB). Since basic configurations of a base stationand a terminal according to Embodiment 2 are common to those of basestation 100 and terminal 200 according to Embodiment 1, they will bedescribed with reference to FIGS. 10 and 11.

In base station 100 of Embodiment 2, control signal mapping controlsection 104 identifies a search space corresponding to a pair of thedivision number M calculated in division number calculation section 103and an aggregation level based on the division number M, the “searchspace information” received from search space determining section 102and the aggregation level.

To be more specific, a search space is identified based on a “VRBtable,” the division number M, “search space information,” anaggregation level, and an “association rule” per pair of the divisionnumber M and the aggregation level. The search space is made up of aplurality of “resource region candidates” and each “resource regioncandidate” is made up of as many CCEs (hereinafter may also be referredto as “mapping candidate CCEs”) as aggregation levels.

More specifically, as shown in FIG. 12, control signal mapping controlsection 104 includes VRB table storage section 121, search spaceidentification section 122 and mapping resource selection section 123.

VRB table storage section 121 stores a “VRB table.” The “VRB table”associates a plurality of VRB pairs with a divided resource region (thatis, “virtual channel CCE”) group per division number candidate of eachVRB pair. The “VRB table” further associates a plurality of pairs of thedivision number candidate and aggregation level candidate with aplurality of “virtual channel unit resource region candidates” inaccordance with each pair. Each “virtual channel unit resource regioncandidate” is made up of as many “virtual channel CCEs used” asaggregation levels.

Search space identification section 122 identifies the virtual channelCCE group used associated in the VRB table with a pair of the divisionnumber M calculated in division number calculation section 103 and theaggregation level. Search space identification section 122 thenidentifies a search space of the physical channel based on theidentified virtual channel CCE group used, “search space information”received from search space determining section 102 and an “associationrule” corresponding to the pair of the division number M calculated indivision number calculation section 103 and the aggregation level. The“association rule” associates a “virtual channel unit resource regioncandidate” with a “physical channel resource region candidate.” Theidentified search space is made up of a plurality of “resource regioncandidates” and each “resource region candidate” is made up of as many“physical channel CCEs used” as aggregation levels. The “physicalchannel CCE used” means the same as the above-described “mappingcandidate CCE.”

In the “VRB table,” the “unit resource region candidate” correspondingto the pair of the division number M and aggregation level L is commonto the “unit resource region candidate” corresponding to the pair of thedivision number 2M and aggregation level 2L. Furthermore, the“association rule” corresponding to the pair of the division number Mand aggregation level L is common to the “association rule”corresponding to the pair of the division number 2M and aggregationlevel 2L.

Mapping resource selection section 123 selects one of the plurality of“resource region candidates” forming the search space identified bysearch space identification section 122 as a control signal mappingresource.

In terminal 200 of Embodiment 2, extracted resource identificationsection 206 identifies a plurality of “resource region groups to beextracted” (that is, search spaces) corresponding to the pair of thedivision number M calculated in division number calculation section 205and an aggregation level based on the division number M, the searchspace information transmitted from base station 100 and the aggregationlevel.

To be more specific, a search space is identified based on the “VRBtable,” the division number M, the “search space information,” theaggregation level, and the “association rule” per pair of the divisionnumber M and the aggregation level. Each search space is made up of aplurality of “resource regions to be extracted” and each “resourceregion to be extracted” is made up of as many CCEs (hereinafter, mayalso be referred to as “CCEs to be extracted”) as aggregation levels.

More specifically, extracted resource identification section 206includes VRB table storage section 221 and search space identificationsection 222 as shown in FIG. 13.

VRB table storage section 221 stores the same “VRB table” as that ofbase station 100. That is, the “VRB table” associates a plurality of VRBpairs with a divided resource region (that is, “virtual channel CCE”)group per division number candidate of each VRB pair. The “VRB table”further associates the plurality of pairs of division number andaggregation level candidates with the plurality of “virtual channelresource regions to be extracted” corresponding to each pair. Each“virtual channel resource region to be extracted” is made up of as many“virtual channel CCE used” as aggregation levels.

Search space identification section 222 identifies a virtual channel CCEgroup used associated in the VRB table with the pair of the divisionnumber M calculated in division number calculation section 205 and theaggregation level. Search space identification section 222 thenidentifies a search space of the physical channel based on theidentified virtual channel CCE group used, the “search spaceinformation,” and the “association rule” corresponding to the pair ofthe division number M calculated in division number calculation section205 and the aggregation level. The “association rule” associates a“virtual channel resource region to be extracted” with a “physicalchannel resource region to be extracted.” The identified search space ismade up of a plurality of “resource regions to be extracted” and each“resource region to be extracted” is made up of as many “physicalchannel CCEs used” as aggregation levels. The “physical channel CCEused” means the same as the above-described “CCE to be extracted.”

Here, the “unit resource region candidate” corresponding to the pair ofthe division number M and aggregation level L in the “VRB table” iscommon to the “unit resource region candidate” corresponding to the pairof the division number 2M and aggregation level 2L. Furthermore, the“association rule” corresponding to the pair of the division number Mand aggregation level L is common to the “association rule”corresponding to the pair of the division number 2M and aggregationlevel 2L.

The operations of base station 100 and terminal 200 configured in themanner described above will be described. Here, in particular, a casewill be described as an example where the division number=2 and thedivision number=4. FIG. 14 is a diagram provided for describing theoperations of base station 100 and terminal 200.

The diagram on the left of FIG. 14 visually expresses contents of the“VRB table.” In the “VRB table” shown in FIG. 14, there are fouraggregation levels: levels 1, 2, 4 and 8. Search spaces at levels 1, 2,4 and 8 have 6, 6, 2 and 2 “virtual channel unit resource regioncandidates” respectively. Four virtual channel CCEs obtained by dividingVRB#X which is one VRB pair into 4 are called VRB#X(a), VRB#X(b),VRB#X(c) and VRB#X(d). On the other hand, four physical channel CCEsobtained by dividing PRB#X which is one PRB pair into 4 are calledPRB#X(a), PRB#X(b), PRB#X(c) and PRB#X(d). Two virtual channel CCEsobtained by dividing VRB#X which is one VRB pair into 2 are calledVRB#X(A) and VRB#X(B). On the other hand, two physical channel CCEsobtained by dividing PRB#X which is one PRB pair into 2 are calledPRB#X(A) and PRB#X(B).

The “VRB table” in FIG. 14 includes eight VRB pairs: VRB#0 to VRB#7. Forsearch spaces, as many “virtual channel unit resource region candidates”as aggregation levels are continuously arranged in eight VRB pairs fromVRB#0. In the “VRB table” in FIG. 14, a resource combining VRB#X(a) andVRB#X(b) is VRB#X(A) and a resource combining VRB#X(c) and VRB#X(d) isVRB#X(B).

Search space identification section 122 identifies a virtual channel CCEgroup used associated in the VRB table with a pair of the divisionnumber M calculated in division number calculation section 103 and theaggregation level.

For example, when the division number=4 and the aggregation level=1,VRB#0(a), VRB#0(b), VRB#0(c), VRB#X0(d), VRB#1(a) and VRB#1(b) areidentified as a virtual channel CCE group used. Note that when theaggregation level=1, the virtual channel CCE used is equal to the“virtual channel unit resource region candidate.”

For example, when the division number=4 and the aggregation level=2,VRB#0(a), VRB#0(b), VRB#0(c), VRB#X0(d), VRB#1(a), VRB#1(b), VRB#1(c),VRB#X1(d), VRB#2(a), VRB#2(b), VRB#2(c) and VRB#X2(d) are identified asa virtual channel CCE group used. On the other hand, when the divisionnumber=2 and the aggregation level=1, VRB#0(A), VRB#0(B), VRB#1(A),VRB#1(B), VRB#2(A) and VRB#2(B) are identified as a virtual channel CCEgroup used. As described above, a resource combining VRB#X(a) andVRB#X(b) is VRB#X(A) and a resource combining VRB#X(c) and VRB#X(d) isVRB#X(B) in the “VRB table.” The “virtual channel unit resource regioncandidate” in the case where the division number=4 and the aggregationlevel=2 matches that in the case where the division number=2 and theaggregation level=1.

When the division number=4 and aggregation level=4, VRB#0(A), VRB#0(B),VRB#1(A), VRB#1(B), VRB#2(A), VRB#2(B), VRB#3(A), VRB#3(B), VRB#4(A),VRB#4(B), VRB#5(A) and VRB#5(B) are identified as a virtual channel CCEgroup used. At this time, the “virtual channel unit resource regioncandidates” are {VRB#0(A), VRB#0(B)}, {VRB#1(A), VRB#1(B)}, {VRB#2(A),VRB#2(B)}, {VRB#3(A), VRB#3(B)}, {VRB#4(A), VRB#4(B)}, and {VRB#5(A),VRB#5(B)}. Here, a set of VRBs enclosed by {} makes up one “virtualchannel unit resource region candidate.” The “virtual channel unitresource region candidate” in the case where the division number=4 andthe aggregation level=4 matches that in the case where the divisionnumber=2 and the aggregation level=2. However, when the divisionnumber=4 and the aggregation level=4, since there are two “virtualchannel unit resource region candidates,” only {VRB#0(A), VRB#0(B)} and{VRB#1(A), VRB#1(B)} are used.

When the division number=4 and the aggregation level=8, VRB#0(A),VRB#0(B), VRB#1(A), VRB#1(B), VRB#2(A), VRB#2(B), VRB#3(A), and VRB#3(B)are identified as a virtual channel CCE group used. At this time, thereare two “virtual channel unit resource region candidates”: {VRB#0(A),VRB#0(B), VRB#1(A), VRB#1(B)} and {VRB#2(A), VRB#2(B), VRB#3(A),VRB#3(B)}. The “virtual channel unit resource region candidate” in thecase where the division number=4 and the aggregation level=8 matchesthat in the case where the division number=2 and the aggregationlevel=4.

When the division number=2 and the aggregation level=8, the “virtualchannel unit resource region candidates” are {VRB#0(A), VRB#0(B),VRB#1(A), VRB#1(B), VRB#2(A), VRB#2(B), VRB#3(A), VRB#3(B)}, and{VRB#4(A), VRB#4(B), VRB#5(A), VRB#5(B), VRB#6(A), VRB#6(B), VRB#7(A),VRB#7(B)}.

Search space identification section 122 identifies a search space of thephysical channel based on the identified virtual channel CCE group used,“search space information” received from search space determiningsection 102, and the “association rule” corresponding to the pair of thedivision number M calculated in division number calculation section 103and the aggregation level.

For example, when the division number=4 and the aggregation level=2, asshown in the diagram in the middle of FIG. 14, VRB#0(A), VRB#0(B),VRB#1(A), VRB#1(B), VRB#2(A) and VRB#2(B) are mapped to PRB#0(A),PRB#1(A), PRB#2(A), PRB#3(A), PRB#4(A) and PRB#4(B) according to the“association rule.” When the division number=2 and the aggregationlevel=1, as shown in the diagram on the right of FIG. 14, VRB#0(A),VRB#0(B), VRB#1(A), VRB#1(B), VRB#2(A) and VRB#2(B) are mapped toPRB#0(A), PRB#1(A), PRB#2(A), PRB#3(A), PRB#4(A) and PRB#4(B) accordingto the “association rule.” That is, the “association rule” in the casewhere the division number=4 and the aggregation level=2 matches that inthe case where the division number=2 and the aggregation level=1.

On the other hand, terminal 200 performs processing similar to that ofbase station 100. That is, search space identification section 222identifies the virtual channel CCE group used associated in the VRBtable with the pair of the division number M calculated in divisionnumber calculation section 205 and the aggregation level. Search spaceidentification section 222 identifies a search space of the physicalchannel based on the identified virtual channel CCE group used, “searchspace information” and the “association rule” corresponding to the pairof the division number M calculated in division number calculationsection 205 and the aggregation level.

As described above, according to the present embodiment, control signalmapping control section 104 in base station 100 determines a searchspace by determining a control channel element group forming a pluralityof resource region candidates among CCE groups obtained by dividing eachPRB pair included in the first group into the same number as thedivision number. The plurality of resource region candidates are commonwhen the division number is M (M is a natural number) and the value ofthe aggregation level is A (A is a natural number) and when the divisionnumber is 2M and the value of the aggregation level is 2A.

Even when the division number of a PRB pair varies from one subframe toanother, assignment of physical resources can be made common in thisway, and it is thereby possible to reduce the amount of signaling whenbase station 100 indicates the physical resources to terminal 200.Furthermore, if a PRB pair having good quality is included in the firstgroup in the first subframe, it is possible to continue to use the PRBpair even when the division number varies from one subframe to another.

According to the present embodiment, extracted resource identificationsection 206 in terminal 200 identifies a search space by identifying acontrol channel element group forming a plurality of resource regioncandidates in the CCE group obtained by dividing each PRB pair includedin the first group into the same number as the division number. Theplurality of resource region candidates forming the identified searchspace correspond to the plurality of “resource regions to be extracted.”The plurality of “resource regions to be extracted” are common when thedivision number is M (M is a natural number) and the value of theaggregation level is A (A is a natural number) and when the divisionnumber is 2M and the value of the aggregation level is 2A.

Embodiment 3

Embodiment 3 relates to variations of a method for mapping a logicalchannel (VRB) to a physical channel (PRB). Note that since basicconfigurations of a base station and a terminal according to Embodiment3 are common to those of base station 100 and terminal 200 according toEmbodiment 1 and Embodiment 2, they will be described with reference toFIGS. 10 and 11.

In base station 100 according to Embodiment 3, control signal mappingcontrol section 104 identifies a search space corresponding to a pair ofthe division number M calculated in division number calculation section103 and an aggregation level based on the division number M, the “searchspace information” received from search space determining section 102and the aggregation level.

To be more specific, a search space is identified based on a “VRBtable”, the division number M, “search space information,” aggregationlevel, a “first type association rule” and a “second type associationrule.” Here, the “first type association rule” is a rule that associates“virtual channel unit resource region candidates” with “physical channelunit resource region candidates” regarding the pair of the divisionnumber M/2 and the aggregation level as in the case of Embodiment 2. Onthe other hand, the “second type association rule” is a rule thatassociates “resource region candidates” regarding the pair of thedivision number M/2 and the aggregation level with “resource regioncandidates” regarding the pair of the division number M and theaggregation level. That is, the “second type association rule” is a rulethat associates “physical channel CCEs” regarding the division numberM/2 with “physical channel CCEs” regarding the division number M in agiven PRB pair. Here, in the case of the division number M, up to M/2 ofM physical channel CCEs included in one PRB pair may be designated asphysical channel CCEs used.

More specifically, control signal mapping control section 104 includessearch space identification section 132 as shown in FIG. 15.

Search space identification section 132 identifies a virtual channel CCEgroup used associated in the VRB table with the pair of the “referencedivision number” and the aggregation level. Search space identificationsection 132 identifies a search space of the physical channelcorresponding to the pair of the “reference division number” and theaggregation level based on the identified virtual channel CCE groupused, the “search space information” and the “first type associationrule” corresponding to the pair of the “reference division number” andthe aggregation level. Here, when the division number calculated indivision number calculation section 103 is 2M, the “reference divisionnumber” is M.

Search space identification section 132 identifies a search space of thephysical channel corresponding to the division number calculated indivision number calculation section 103 based on the search space of thephysical channel corresponding to the pair of the “reference divisionnumber” and the aggregation level, and the “second type associationrule.”

Extracted resource identification section 206 in terminal 200 ofEmbodiment 3 identifies a plurality of “resource region groups to beextracted” (that is, search space) corresponding to the pair of thedivision number M calculated in division number calculation section 205and an aggregation level based on the division number M, the searchspace information transmitted from base station 100 and the aggregationlevel.

To be more specific, a search space is identified based on the “VRBtable,” the division number M, “search space information,” aggregationlevel, “first type association rule” and “second type association rule.”Here, the “first type association rule” is a rule that associates the“virtual channel resource regions to be extracted” with the “physicalchannel resource regions to be extracted” regarding the pair of thedivision number M/2 and aggregation level as in the case of Embodiment2. On the other hand, the “second type association rule” is a rule thatassociates the “physical channel resource regions to be extracted”regarding the pair of the division number M/2 and aggregation level withthe “physical channel resource regions to be extracted” regarding thepair of the division number M and aggregation level. That is, the“second type association rule” is a rule that associates the “physicalchannel CCEs” regarding the division number M/2 with the “physicalchannel CCEs” regarding the division number M in a given PRB pair.

More specifically, extracted resource identification section 206includes search space identification section 232 as shown in FIG. 16.

Search space identification section 232 identifies a virtual channel CCEgroup used associated in the VRB table with the pair of the “referencedivision number,” i.e., the division number M and the aggregation level.Search space identification section 232 identifies a search space of thephysical channel corresponding to the pair of the “reference divisionnumber” and the aggregation level based on the identified virtualchannel CCE group used, “search space information” and the “first typeassociation rule” corresponding to the pair of the “reference divisionnumber” and the aggregation level.

Search space identification section 232 identifies a search space of thephysical channel corresponding to the division number calculated indivision number calculation section 205 based on the search space of thephysical channel corresponding to the pair of the “reference divisionnumber” and the aggregation level, and the “second type associationrule.”

The operations of base station 100 and terminal 200 configured in themanner described above will be described. Here, in particular, a casewill be described as an example where the division number=2 and thedivision number=4. FIG. 17 is a diagram provided for describing theoperations of base station 100 and terminal 200.

The diagram on the left of FIG. 17 visually expresses contents of a “VRBtable” when the division number=4.

When the division number=2 calculated in division number calculationsection 205, search space identification section 132 identifies avirtual channel CCE group used associated in the VRB table with the pairof the reference division number=4 and the aggregation level using the“VRB table” shown in the diagram on the left of FIG. 17.

Search space identification section 132 identifies a search space of thephysical channel corresponding to the pair of the reference divisionnumber=4 and the aggregation level based on the identified virtualchannel CCE group used, “search space information” and the “first typeassociation rule” corresponding to the pair of the reference divisionnumber=4 and the aggregation level. For example, when the divisionnumber=4 and the aggregation level=2, as shown in the diagram in themiddle of FIG. 17, VRB#0(A), VRB#0(B), VRB#1(A), VRB#1(B), VRB#2(A) andVRB#2(B) are mapped to PRB#0(A), PRB#1(A), PRB#2(A), PRB#3(A), PRB#4(A)and PRB#4(B) according to the “first type association rule.”

Search space identification section 132 then identifies a search spaceof the physical channel corresponding to the division number calculatedin division number calculation section 103 based on the search space ofthe physical channel corresponding to the pair of the “referencedivision number” and the aggregation level, and the “second typeassociation rule.” Here, according to “second type association rule” inFIG. 17, PRB#X(a) and PRB#X(c) are associated with PRB#X(A), andPRB#X(b) and PRB#X(d) are associated with PRB#X(B). However, PRB#X(a)and PRB#X(c) associated with PRB#X(A) are never used simultaneously asphysical channel CCEs used. Similarly, PRB#X(b) and PRB#X(d) associatedwith PRB#X(B) are never used simultaneously as physical channel CCEsused.

Search space identification section 232 of terminal 200 performbasically the same operation as that of search space identificationsection 132.

As described above, according to the present embodiment, control signalmapping control section 104 in base station 100 determines a searchspace by determining a control channel element group forming a pluralityof resource region candidates among CCE groups obtained by dividing eachPRB pair included in the first group into the same number as thedivision number. Control signal mapping control section 104 thenidentifies a second search space in the physical channel when thedivision number is 2M (M is a natural number) and the value of theaggregation level is 2A (A is a natural number) based on the firstsearch space in the logical channel and the first type association rulewhen the division number is 2M and the value of the aggregation level is2A. Control signal mapping control section 104 further identifies athird search space in the physical channel when the division number is Mand the value of the aggregation level is A based on the second searchspace and the second type association rule. The second type associationrule associates CCEs when the division number in each PRB pair is 2Mwith CCEs when the division number is M.

By so doing, even when the division number of a PRB pair varies from onesubframe to another, if base station 100 indicates physical resources toterminal 200 for the division number 2M, indication for the divisionnumber M is unnecessary, and it is thereby possible to reduce the amountof signaling when base station 100 indicates physical resources toterminal 200. If a PRB pair of good quality is included in the firstgroup in the first subframe, it is possible to continue to use the PRBpair even when the division number varies from one subframe to another.

According to the present embodiment, extracted resource identificationsection 206 in terminal 200 identifies a search space by identifying acontrol channel element group forming a plurality of resource regioncandidates among CCE groups obtained by dividing each PRB pair includedin the first group into the same number as the division number. Theplurality of resource region candidates forming this identified searchspace, correspond to the plurality of “resource regions to beextracted.” Extracted resource identification section 206 thenidentifies a second search space in the physical channel when thedivision number is 2M (M is a natural number) and the value of theaggregation level is 2A (A is a natural number) based on the firstsearch space in the logical channel and the first type association rulewhen the division number is 2M and the value of the aggregation level is2A. Furthermore, extracted resource identification section 206identifies a third search space in the physical channel when thedivision number is M and the value of the aggregation level is A basedon the second search space and the second type association rule. Thesecond type association rule associates CCEs when the division number ineach PRB pair is 2M with CCEs when the division number is M.

Embodiment 4

As with Embodiment 3, Embodiment 4 relates to a variation of a methodfor mapping a logical channel (VRB) to a physical channel (PRB).However, the relationship between the calculated division number and the“reference division number” in Embodiment 4 is opposite to therelationship in Embodiment 3. Since basic configurations of a basestation and a terminal according to Embodiment 4 are common to those ofbase station 100 and terminal 200 according to Embodiment 1 andEmbodiment 3, they will be described with reference to FIGS. 10, 11, 15and 16.

In base station 100 of Embodiment 4, search space identification section132 identifies a virtual channel CCE group used associated in a VRBtable with a pair of the “reference division number” and the aggregationlevel. Search space identification section 132 identifies a search spaceof the physical channel corresponding to the pair of the “referencedivision number” and the aggregation level based on the identifiedvirtual channel CCE group used, “search space information” and the“first type association rule” corresponding to the pair of the“reference division number” and the aggregation level. Here, when thedivision number calculated in division number calculation section 103 isM, the “reference division number” is 2M.

Search space identification section 132 identifies a search space of thephysical channel corresponding to the division number calculated indivision number calculation section 103 based on the search space of thephysical channel corresponding to the pair of the “reference divisionnumber” and the aggregation level, and the “second type associationrule.”

In terminal 200 of Embodiment 4, search space identification section 232identifies a virtual channel CCE group used associated in a VRB tablewith the pair of the “reference division number,” i.e., the divisionnumber M and the aggregation level. Search space identification section232 then identifies a search space of the physical channel correspondingto the pair of the “reference division number” and the aggregation levelbased on the identified virtual channel CCE group used, “search spaceinformation” and the “first type association rule” corresponding to thepair of the “reference division number” and the aggregation level.

Search space identification section 232 then identifies a search spaceof the physical channel corresponding to the division number calculatedin division number calculation section 205 based on a search space ofthe physical channel corresponding to the pair of the “referencedivision number” and the aggregation level, and the “second typeassociation rule.”

The operations of base station 100 and terminal 200 configured in themanner described above will be described. Here, in particular, a casewill be described as an example where the division number=2 and thedivision number=4. FIG. 18 is a diagram provided for describing theoperations of base station 100 and terminal 200.

When the division number=4 calculated in division number calculationsection 205, search space identification section 132 identifies avirtual channel CCE group used associated in the VRB table with the pairof the reference division number=2 and the aggregation level using the“VRB table” shown in the diagram on the left of FIG. 18.

Search space identification section 132 identifies a search space of thephysical channel corresponding to the pair of the reference divisionnumber=2 and the aggregation level based on the identified virtualchannel CCE group used, “search space information” and the “first typeassociation rule” corresponding to the pair of the reference divisionnumber=2 and the aggregation level. For example, when the divisionnumber=2 and the aggregation level=2, as shown in the diagram in themiddle of FIG. 17, VRB#0(A), VRB#0(B), VRB#1(A), VRB#1(B), VRB#2(A),VRB#2(B), VRB#3(A), VRB#3(B), VRB#4(A), VRB#4(B), VRB#5(A) and VRB#5(B)are mapped to PRB#0(A), PRB#0(B), PRB#1(A), PRB#1(B), PRB#3(A),PRB#3(B), PRB#4(A), PRB#4(B), PRB#6(A), PRB#6(B), PRB#7(A) and PRB#7(B)according to the “first type association rule.”

Search space identification section 132 then identifies a search spaceof the physical channel corresponding to the division number calculatedin division number calculation section 103 based on a search space ofthe physical channel corresponding to the pair of the “referencedivision number” and the aggregation level, and the “second typeassociation rule”. The “second type association rule” in FIG. 17associates PRB#X(A) with PRB#X(a) and associates PRB#X(B) with PRB#X(c)in PRB#0 or the like. On the other hand, the “second type associationrule” in FIG. 17 associates PRB#X(A) with PRB#X(b) and associatesPRB#X(B) with PRB#X(d) in PRB#6 or the like. That is, the method ofassociation is changed between the first PRB pair and the second PRBpair. However, the “second type association rule” is not limited to thisexample, and a common method of association may be used between thefirst PRB pair and the second PRB pair.

Search space identification section 232 of terminal 200 performbasically the same operation as that of search space identificationsection 132.

As described above, according to the present embodiment, control signalmapping control section 104 in base station 100 determines a searchspace by determining a control channel element group forming a pluralityof resource region candidates among CCE groups obtained by dividing eachPRB pair included in the first group into the same number as thedivision number. Control signal mapping control section 104 identifies asecond search space in the physical channel when the division number isM (M is a natural number) and the value of the aggregation level is A (Ais a natural number) based on the first search space in the logicalchannel and the first type association rule when the division number isM and the value of the aggregation level is A. Control signal mappingcontrol section 104 identifies a third search space in the physicalchannel when the division number is 2M and the value of the aggregationlevel is 2A based on the second search space and the second typeassociation rule. The second type association rule associates controlchannel elements when the division number is 2M in each physical channelresource block with control channel elements when the division number isM.

By so doing, even when the division number of a PRB pair varies from onesubframe to another, if base station 100 indicates physical resources toterminal 200 for the division number M, indication for the divisionnumber 2M becomes unnecessary, and it is thereby possible to reduce theamount of signaling when base station 100 indicates physical resourcesto terminal 200. Furthermore, if a PRB pair of good quality is includedin the first group in the first subframe, it is possible to continue touse the PRB pair even when the division number varies from one subframeto another.

According to the present embodiment, extracted resource identificationsection 206 in terminal 200 identifies a search space by identifying acontrol channel element group forming a plurality of resource regioncandidates among CCE groups obtained by dividing each PRB pair includedin the first group into the same number as the division number. Theplurality of resource region candidates forming the identified searchspace, correspond to a plurality of “resource regions to be extracted.”Extracted resource identification section 206 identifies a second searchspace in the physical channel when the division number is M (M is anatural number) and the value of the aggregation level is A (A is anatural number) based on the first search space in the logical channeland the first type association rule when the division number is M andthe value of the aggregation level is A. Furthermore, extracted resourceidentification section 206 identifies a third search space in thephysical channel when the division number is 2M and the value of theaggregation level is 2A based on the second search space and the secondtype association rule. The second type association rule associatescontrol channel elements when the division number is 2M in each physicalchannel resource block with control channel elements when the divisionnumber is M.

Other Embodiments

[1] In the above embodiments, the division number may also be determinedbased on the type of subframe. The following are methods for determiningthe division number based on the type of subframe.

(1) The division number is made greater in MBSFN subframes than innon-MBSFN subframes. This makes it possible to increase the divisionnumber of MBSFN subframes having more REs than non-MBSFN subframes andimprove resources utilization efficiency in MBSFN subframes.

(2) The division number is made greater in subframes in which CSI-RS istransmitted than in subframes in which CSI-RS is not transmitted.

(3) The division number is made greater in DL subframes than in specialsubframes. (4) The division number is made greater in subframes having anormal CP length than in subframes having an extended CP length.

(5) The division number is made greater in subframes of extensioncarriers than in subframes of carriers other than extension carriers.The extension carrier is a subframe having no signal regions set foreach cell such as CRS, PDCCH, PHICH or PCFICH.

(6) The division number is made greater in subframes whose number ofOFDM symbols used for PDCCH is three or four than in subframes whosenumber of OFDM symbols used for PDCCH is one.

(7) When the cell to which the terminal is connected sets ABS (almostblank subframe), the division number is made smaller in ABS than innon-ABS subframes. Transmitting an ABS with small transmission power soas not to provide interference to other cells causes channel quality ofthe ABS to degrade. The division number is made smaller in subframes oflow channel quality.

(8) When a cell that provides interference to the cell to which theterminal is connected sets ABS (almost blank subframe), the divisionnumber is made smaller in non-ABS subframes than ABS. Channel qualityincreases in subframes set by the other cell as an ABS and channelquality degrades in subframes not set as an ABS. The division number ismade smaller in non-ABS subframes of low channel quality. Reducing thedivision number in subframes whose channel quality degrades allowschannel quality of a control signal to improve.

[2] The above embodiments have been described on the assumption thatlogical channels are mapped continuously, but the present invention isnot limited to this assumption, and logical channels may not be mappedcontinuously.

[3] In the above embodiments, the starting positions of search spaces ofthe respective aggregation levels are the same, but the presentinvention is not limited to this case and the starting positions maydiffer.

[4] The above embodiments have been described on the assumption thatsearch spaces of levels 1, 2, 4 and 8 have six, six, two and two“virtual channel unit resource region candidates” respectively, but thenumbers of the candidates are not limited to these numbers. Furthermore,the aggregation level is not limited to this case either.

[5] The above embodiments have been described on the assumption that aPRB pair is divided in the frequency axis direction, but the divisiondirection is not limited to this. That is, the PRB pair may also bedivided in the code axis direction or time axis direction.

[6] The above embodiments can be combined.

(1) For example, when the division number is 1 or 2, one of Embodiments1 to 4 is used. When the division number is 4, Embodiment 4 is used tothereby identify a search space with the division number 4 from a searchspace with the division number 2.

(2) For example, when the division number is 1 or 2, one of Embodiments1 to 4 is used. When the division number is 4, Embodiment 2 is used.However, the search space when the division number is 4 and theaggregation level is 1 is obtained by dividing into two the search spacewhen the division number is 4 and the aggregation level is 2.

(3) For example, when the division number is 2 or 4, one of Embodiments1 to 4 is used. When the division number is 1, Embodiment 3 is used tothereby identify a search space with the division number 1 from a searchspace with the division number 2. In this case, however, when thedivision number is 2, PRB pairs are assigned so that one search spaceper PRB may be assigned.

(4) For example, when the division number is 2 or 4, one of Embodiments1 to 4 is used. When the division number is 1, Embodiment 2 is used. Asearch space when the division number is 1 and the aggregation level is8 may be assumed to be a combination of two search spaces when thedivision number is 2 and the aggregation level is 8.

[7] The embodiments of the present invention described above areprovided as hardware. The present invention can be achieved throughsoftware in cooperation with hardware.

The functional blocks described in the embodiments are achieved by anLSI, which is typically an integrated circuit. The functional blocks maybe provided as individual chips, or part or all of the functional blocksmay be provided as a single chip. Depending on the level of integration,the LSI may be referred to as an IC, a system LSI, a super LSI, or anultra LSI.

In addition, the circuit integration is not limited to LSI and may beachieved by dedicated circuitry or a general-purpose processor otherthan an LSI. After fabrication of LSI, a field programmable gate array(FPGA), which is programmable, or a reconfigurable processor whichallows reconfiguration of connections and settings of circuit cells inLSI may be used.

Should a circuit integration technology replacing LSI appear as a resultof advancements in semiconductor technology or other technologiesderived from the technology, the functional blocks could be integratedusing such a technology. Another possibility is the application ofbiotechnology and/or the like.

The disclosure of Japanese Patent Application No. 2011-176855, filed onAug. 12, 2011, including the specification, drawings and abstract, isincorporated herein by reference in its entirety.

INDUSTRIAL APPLICABILITY

The transmitting apparatus, receiving apparatus, transmission method,and reception method of the present invention are useful in improvingreceiving quality of a control signal.

REFERENCE SIGNS LIST

-   100 Base station-   101 Assignment control information generating section-   102 Search space determining section-   103, 205 Division number calculation section-   104 Control signal mapping control section-   105, 208 Error-correction coding section-   106, 209 Modulation section-   107, 210 Mapping section-   108, 211 Transmitting section-   109, 201 Receiving section-   110, 203 Demodulation section-   111, 204 Error-correction decoding section-   121, 221 VRB table storage section-   122, 132, 222, 232 Search space identification section-   123 Mapping resource selection section-   200 Terminal-   202 Signal demultiplexing section-   206 Extracted resource identification section-   207 Control signal receiving section

The invention claimed is:
 1. A communication apparatus comprising:control circuitry which, in operation, configures a plurality ofresource region candidates based on a division number which is a numberof Control Channel Elements (CCEs) per resource block pair, eachresource region candidate including at least one CCE, wherein thedivision number is larger for a subframe having a normal cyclic prefixlength than for a subframe having an extended cyclic prefix length; anda transmitter which, in operation, maps downlink control information toone of the plurality of resource region candidates and, in operation,transmits the mapped downlink control information.
 2. The communicationapparatus according to claim 1, wherein the plurality of resource regioncandidates are configured in an Extended Physical Downlink ControlCHannel (EPDCCH) that is a resource region defined in a data region of asubframe.
 3. The communication apparatus according to claim 1, whereinthe division number for a downlink normal subframe is larger than thedivision number for a special subframe having a gap period for switchingbetween a downlink and an uplink.
 4. The communication apparatusaccording to claim 1, wherein the resource block pair comprises twoslots.
 5. The communication apparatus according to claim 1, wherein eachCCE includes a plurality of resource elements.
 6. The communicationapparatus according to claim 1, wherein the division number is acquiredby dividing a specified number by a number of resource elements includedin one CCE.
 7. A communication method comprising: configuring aplurality of resource region candidates based on a division number whichis a number of Control Channel Elements (CCEs) per resource block pair,each resource region candidate including at least one CCE, wherein thedivision number is larger for a subframe having a normal cyclic prefixlength than for a subframe having an extended cyclic prefix length;mapping downlink control information to one of the plurality of resourceregion candidates; and transmitting the mapped downlink controlinformation.
 8. The communication method according to claim 7, whereinthe plurality of resource region candidates are configured in anExtended Physical Downlink Control CHannel (EPDCCH) that is a resourceregion defined in a data region of a subframe.
 9. The communicationmethod according to claim 7, wherein the division number for a downlinknormal subframe is larger than the division number for a specialsubframe having a gap period for switching between a downlink and anuplink.
 10. The communication method according to claim 7, wherein theresource block pair comprises two slots.
 11. The communication methodaccording to claim 7, wherein each CCE includes a plurality of resourceelements.
 12. The communication method according to claim 7, wherein thedivision number is acquired by dividing a specified number by a numberof resource elements included in one CCE.